1. FIELD OF THE INVENTION
This invention relates to an optical storage disk, card or device and in particular a method for the manufacture thereof.
2. DESCRIPTION OF THE PRIOR ART
Existing optical disk or card art relating to write once-read many (WORM), magneto-optical (erasable) type or similar optical recording devices generally consists of a laminated or multilayered structure having a rigid support substrate, a reflective layer, a photosensitive optically reactive second surface layer which is, depending upon disk or card application, covered by a first surface optically transparent protective coating layer. Historically each said layer has been subsequently superimposed intermittently upon the preceding layer on a disk by disk basis, by various succeeding methods such as injection or compression molding, spin coating, sputtering, vacuum deposition, and, in general, by means of individual layer by layer lamination techniques. Each substrate is processed to receive succeeding such lamination coatings individually, serially or in batches of small numbers. More recent trends in optical recording technology have led to development of first surface optically recordable laminations which have been conveniently and efficiently manufactured in a continuous, rather than intermittent, process in wide webs of great length and width in a manner analogous to conventional manufacture of magnetic tape. By such means, optical recording laminations may likewise be manufactured in an efficient and economical process. However, although such first surface optically recording laminations may be cut into circular or rectangular sheets as well as traditional lengthy tapes, the relatively thin, first surface optically recordable disks or cards produced in such manner have significant disadvantages when compared to earlier second surface optical recording structures.
In spite of a thin protective coating over the first surface optically reactive layer of such laminated sheets, randomly attracted dust particles of but a micron or so in diameter, not visible to the unaided eye, may lodge very close to the first surface optically reactive layer, thereby blocking out significant areas of the optically reactive layer causing commensurate dropouts of data recorded and reproduced with subsequent loss of information.
In addition, the relatively thin laminate sheet structure of optical disks cut from an optical laminate sheet has no rigid structural component and therefore has a tendency to bend and curl. Therefore, it is necessary that such laminate optical recording disks be spun immediately above a flat stationary surface at a speed above a critical minimum which flattens the disk to optical record/reproduce requirements by formation of an air bearing film, generally referred to as the Bernoulli approach.
There exists therefore a longstanding and continuing need for a new and improved optical recording disk having the rigid, second surface optical attributes of a thick and transparent substrate and therefore a surface which will hold dust and mechanical defects at a safe distance from the plane of a focussed record/reproduce beam on the recordable layer, yet also having the economical manufacturing advantages of a first surface optical lamination of large sheets of an optical recording medium. The invention disclosed herein does just that by combining the technical advantages of a second surface optical medium together with the manufacturing simplicity and efficiency of a first surface optical recording medium.